It is often necessary to transmit data or control signals using telephonic circuits, and more generally low current transmission circuits, which can be submitted to various origin disturbances and particularly disturbances of atmospheric origin.
The energy of the disturbances has a considerable influence on the accuracy of the transmitted signals and also on the circuits and equipments placed at the ends of the circuits for the purpose of either transmitting or receiving said signals. Thus phenomena of atmospheric origin produce, on the transmission lines, disturbances having a very important energy and causing, in almost all cases, the destruction of the circuits connected to the line in question.
Various solutions have been offered, especially the incorporation of lightning-protectors in the circuits, but if said solutions are, generally, efficient for the protection of the circuit, they do not, most of the time, prevent the destruction of the apparatus placed at the ends of the lines and nearly always lead to the destruction of the emitting and receiving apparatus respectively placed at each end of the line.
The present invention copes with said disadvantages in providing protective blocks at each end of the transmission circuit, as well on the emitting side as on the receiving side of the signals, whereby totally separating emitting-receiving units from the line properly so-called.
It is known in the art of line protection to use a transformer to separate the emitting-receiving units from the transmission line. However, such transformers themselves transmit a part of the energy of the disturbance from the line to the emitting-receiving units, whereby total true isolation is not properly provided. As a result, the disturbance still may cause destruction of the units.
It then appears that one of the primary purposes of the invention is to protect the transmitter and the receiver if a transmission line is subjected to a strike of lightning. Thus, a transformer or any other close coupling component could not be used as successfully as applicant's protective device in which the totality of isolation for the transmitter and receiver is an important aspect of the invention.